The technology of bearings lies at the heart and construction of machines of all sorts. The desire is to allow relative shear motion between two mating surfaces despite their support of a substantive normal force. Low shear forces are preferred to increase the mechanical efficiency of the machine, reduce frictional heating and wear of the surfaces, and to reduce the formation of wear particles which can interfere with the operation of the machine or contaminate the environment.
There are a variety of bearings in use today. The most basic design of a bearing is one in which the two mating surfaces rub on one another directly. This type of bearings generates heat, and can contaminate the environment when one or both of the surfaces in contact begins to break down. Bearings can be coated with a thin layer of solid low-shear strength material, which localizes the contact regions allowing for easier shearing. However, these bearings still generate heat, have a long life, and do not give a significant shear force. Other designs of bearings employ liquid or solid lubricant between the mating surfaces to provide a lower shear force, and to dissipate heat. Contact of mating surfaces may be inhibited through the use of anisotropic molecular layers. However, these bearings give a significant shear force, and require servicing.
Hydrodynamic bearings, which are formed by squeezing a viscous fluid into a narrowing channel, prevent the mating of surfaces, but fail to operate at low relative velocities, and require routine servicing. Hydrostatic bearings also prevent contact of the mating surfaces through the use of fluid which is pumped through combination of fixed and variable orifices. However, hydrostatic bearings require power for operation, and are expensive to manufacture.
Electrostatic and magnetic bearings prevent contact of mating parts through the use of controlled electrostatic or magnetic fields and forces. Usually, an electronic control system continuously adjusts the fields to compensate for disturbances, particularly when there is no nominal relative velocity of the mating surfaces. However, electrostatic and magnetic bearings require power for operation, do not provide a large normal force, and are expensive to produce.
Flexures are used as an alternative to bearings. Flexures support a load in one direction and allow motion in another. However, flexures have limited displacements and a restraining shear force.
One growing area of use for bearings is in micromachines. Solid flexure member are widely used in micromechanical systems (e.g. microvalves and micropumps) to provide mechanical support and sealing. Various solid flexure constraints have been widely used in micromechanical systems to support members which have small displacement only. The most common examples are slender cantilever beams such as used in comb drives and diaphragms used in pressure sensors. Although these operate well for sensors, flexures are restricting for the output of actuators. Solid-to-solid contact generates unacceptable friction for microstructures which cannot be lubricated in the conventional manner of larger structures, and which can be damaged by the formation of wear particles in the environment. Rolling bearings were employed by Fujita and Omodaha, but only for larger actuators.
As with bearings, check valves have widespread applications. Conventional check valves employ a moveable or flexible solid member which seals upon contact with a valve seat. This design may subject the device to excessive wear. Those with flexible members are typically larger than desired. Therefore, there exists a need to decrease the response time of current check valves.
It is among the objects of the present invention to provide bearings and seals which overcome the limitations associated with prior art bearings, seals and check valves described above.